someone told me that its not in the resinator. that theres one on the engine and one rite after the header
The first is AFTER the collection pipes of the header, so that it works on the gases coming from all 4 cylinders. In many dual-cat vehicles, the first is mid-header" (just after the collection 4-1 section, or whatever the collection form) and the second is a foot to three further back, before the big rearward exhaust tube. In other dual-cat vehicles, there is a "mid-pipe" between the header and the second cat and the second cat is closer to the rear axle. I haven't looked hard enough at the xB's exhaust system to see where they are on it. I'm SURE someone that has replaced all the parts of the exhaust system can tell us precisely where each of the cats are.
Cats are catalytic converters that have catalysts for chemical reactions that neutralize specific exhaust gases deemed "bad" by the people that matter. So, they use catalysts to initiate chemical reactions that convert those gases to "good" and "not as bad" gases. Older cars had NO cats, then they had one from the late 1960s (introduction of exhaust testing) until the 1990s. In the 1990s, they added a SECOND cat. The two are designed to work in tandem and neutralize/convert more "bad" gases to "better" gases.
They are also a "wear" item, so they are designed to be removable and replaced during the life of the vehicle, or at least in ones that are not "disposable." So, there is often a flange with bolts on the front and back sides of the cat itself (so it can be unbolted and replaced quickly and easily).
